Modelling of automotive fuel droplets heating and evaporation - mathematical tools and approximations

New mathematical tools and approximations developed for the analysis of automotive fuel droplet heating and evaporation are summarised. The approach to modelling biodiesel fuel droplets is based on the application of the Discrete Component Model (DCM), while the approach to modelling Diesel fuel droplets is based on the application of the recently developed multi-dimensional quasi-discrete model. In both cases, the models are applied in combination with the Eective Thermal Conductivity/Eective Diusivity model and the implementation in the numerical code of the analytical solutions to heat transfer and species diusion equations inside droplets. It is shown that the approximation of biodiesel fuel by a single component leads to under-prediction of droplet evaporation time by up to 13% which can be acceptable as a crude approximation in some applications. The composition of Diesel fuel was simpli ed and reduced to only 98 components. The approximation of 98 components of Diesel fuel with 15 quasi-components/components leads to under-prediction of droplet evaporation time by about 3% which is acceptable in most engineering applications. At the same time, the approximation of Diesel fuel by a single component and 20 alkane components leads to a decrease in the evaporation time by about 19%, compared with the case of approximation of Diesel fuel with 98 components. The approximation of Diesel fuel with a single alkane quasi-component (C14:763H31:526) leads to under-prediction of the evaporation time by about 35% which is not acceptable even for qualitative analysis of the process. In the case when n-dodecane is chosen as the single alkane component, the above-mentioned under-prediction increases to about 44%

Blended E85-diesel fuel droplet heating and evaporation

The multidimensional quasi-discrete (MDQD) model is applied to the analysis of heating and evaporation of mixtures of E85 (85 vol % ethanol and 15 vol % gasoline) with diesel fuel, commonly known as “E85–diesel” blends, using the universal quasi-chemical functional group activity coefficients model for the calculation of vapor pressure. The contribution of 119 components of E85–diesel fuel blends is taken into account, but replaced with smaller number of components/quasi-components, under conditions representative of diesel engines. Our results show that high fractions of E85–diesel fuel blends have a significant impact on the evolutions of droplet radii and surface temperatures. For instance, droplet lifetime and surface temperature for a blend of 50 vol % E85 and 50 vol % diesel are 23.2% and up to 3.4% less than those of pure diesel fuel, respectively. The application of the MDQD model has improved the computational efficiency significantly with minimal sacrifice to accuracy. This approach leads to a saving of up to 86.4% of CPU time when reducing the 119 components to 16 components/quasi-components without a sacrifice to the main features of the model

Droplets heating and evaporation: an application to diesel-biodiesel fuel mixtures

The heating and evaporation of automotive fuel droplets are crucial to the design of internal combustion engines and to ensuring their good performance. Accurate modelling is essential to the understanding of these processes and ultimately improving engine design. The interest in fossil-biodiesel fuel blends has been mainly stimulated by depletion of fossil fuels and the need to reduce carbon dioxide emissions that contribute towards climate change. This paper presents an analytical investigation into the application of discrete component model for the heating and evaporation of multi-component fuel droplets to several blended diesel-biodiesel fuels. The model considers the contribution of all groups of hydrocarbons in diesel fuel and methyl esters in biodiesel fuels. The main features of new application to the analysis of blended-fuel droplets in engine-like conditions is described. The model is applied to several blends of diesel, combining 98 components of hydrocarbons, and 19 types biodiesel fuels, combining up to 17 species of methyl ester, considering the differences in their chemical levels of saturation, and thermodynamic and transport properties. One important finding is that some fuel blends, e.g. B5 (5% biodiesel fuel and 95% diesel fuel), can give almost identical droplet lifetimes to the one predicted for pure diesel fuel; i.e. such mixtures can be directly used in conventional diesel engines with minimal, or no, modification to the droplet break-up process

Models for automotive fuel droplets heating and evaporation

[EN] The paper presents recent approaches to the modelling of heating and evaporation of automotive fuel droplets with application to biodiesel, diesel, gasoline, and blended fuels in conditions representative of internal combustion engines. The evolutions of droplet radii and temperatures for gasoline, diesel, and a broad range of biodiesel fuels and their selective diesel fuel blends have been predicted using the Discrete Component model (DCM). These mixtures combine up to 112 components of hydrocarbons and methyl esters. The results are compared with the predictions of the case when blended diesel-biodiesel fuel are represented by pure fossil and biodiesel fuels. In contrast to previous studies, it is shown that droplet evaporation time and surface temperature predicted for 100% biodiesel (B100) are not always close to those predicted for pure diesel fuel. Also, the previously introduced MultiDimensional Quasi-Discrete model and its application to these fuels and their mixtures are discussed. The previous application of this model has resulted in up to 96% reduction in CPU time compared to the case when all fuel components are considered using the DCM.The authors are grateful to the Centre for Mobility and Transport – Coventry University for financial support.Al Qubeissi, M.; Sazhin, S.; Al-Esawi, N. (2017). Models for automotive fuel droplets heating and evaporation. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1044-4051. https://doi.org/10.4995/ILASS2017.2017.4754OCS1044405

Ethanol/Gasoline Droplet Heating and Evaporation:Effects of Fuel Blends and Ambient Conditions

This paper focuses on the modeling of blended ethanol/gasoline fuel droplet heating and evaporation in conditions representative of internal combustion engines. The effects of ambient conditions (ambient pressure, ambient temperature, and radiative temperature) and ethanol/gasoline fuel blend ratios on multicomponent fuel droplet heating and evaporation are investigated using the analytical solutions to the heat-transfer and species diffusion equations. The ambient pressures, gas and radiative temperatures, and ethanol/gasoline fuel ratios are considered in the ranges of 3–30 bar, 400–650 K, 1000–2000 K, and 0% (pure gasoline)–100% (pure ethanol), respectively. Transient diffusion of 21 hydrocarbons, temperature gradient, and recirculation inside droplets are accounted for using the <i>discrete component</i> model. The droplet lifetimes of all mixtures decrease when ambient temperatures increase, under all ambient pressures (3–30 bar). The combination of ethanol and gasoline fuels has a noticeable impact on droplet heating and evaporation; for pure ethanol, the predicted droplet surface temperature is 24.3% lower, and lifetime 33.9% higher, than that for gasoline fuel under the same conditions. Finally, taking into account radiation decreases the gasoline fuel droplet evaporation times by up to 28.6%, and those of ethanol fuel droplets by up to 21.8%, compared to the cases where radiation is ignored

A model for mono- and multi-component droplet heating and evaporation and its implementation into ANSYS Fluent

[EN] A model for heating and evaporation of mono- and multi-component droplets, based on analytical solutions to the heat transfer and species diffusion equations in the liquid phase, is summarised. The implementation of the model into ANSYS Fluent via User-Defined Functions (UDF) is described. The model is applied to the analysis of pure acetone, ethanol, and mixtures of acetone/ethanol droplet heating/cooling and evaporation. The predictions of the customised version of ANSYS Fluent with the newly implemented UDF model are verified against the results predicted by the previously developed in house, one-dimensional code.The authors would like to recognise that this work was supported by the UK’s Engineering and Physical Science Research Council, a studentship to support one of the authors (LP) [EPSRC grant EP/N509607/1; EP/K005758/1; EP/K020528/1; EP/M002608/1]Poulton, L.; Rybdylova, O.; Sazhin, SS.; Crua, C.; Qubeissi, M.; Elwardany, AE. (2017). A model for mono- and multi-component droplet heating and evaporation and its implementation into ANSYS Fluent. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 67-74. https://doi.org/10.4995/ILASS2017.2017.4759OCS677

A model for multi-component droplet heating and evaporation and its implementation into ANSYS Fluent

The main ideas of the model for multi-component droplet heating and evaporation, based on the analytical solutions to the heat conduction and species diffusion equations in the liquid phase, and its implementation into ANSYS Fluent CFD software are described. The model is implemented into this software via User-Defined Functions (UDF). The predictions of ANSYS Fluent with the newly implemented model are verified against the results predicted by the previously developed in-house research code for droplets comprising of a mixture of ethanol and acetone evaporating and cooled down in ambient air.Publisher Statement: NOTICE: this is the author’s version of a work that was accepted for publication in International Communications in Heat and Mass Transfer. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in International Communications in Heat and Mass Transfer, [90, (2017)] DOI: 10.1016/j.icheatmasstransfer.2017.10.018© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/<br/

A new model for a drying droplet

A new model for droplet drying is suggested. This model is based on the analytical solutions to the heat transfer and species diffusion equations inside spherical droplets. Small solid particles dispersed in an ambient evaporating liquid, or a non-evaporating substance dissolved in this liquid, are treated as non-evaporating components. Three key sub-processes are involved in the process of droplet drying within the new model: droplet heating/cooling, diffusion of the components inside the droplets, and evaporation of the volatile component. The model is used to analyse the drying of a spray consisting of chitosan dissolved in water. After completion of the evaporation process, the size of the residual solid ball predicted by the model is consistent with those observed experimentally